Electron discharge devices



Oct. 18, 1955 Filed March 9 1951 E. J. SHELTON ELECTRON DISCHARGEDEVICES 2 Sheets-Sheet 1 Oct. 18, 1955 E. J. SHELTON ELECTRON DISCHARGEDEVICES 2 Sheets-Sheet 2 Filed March 9 1951 /n /A/T0/? [an .1 5/952 ro/v19y 6'7- 0 may ilnited States Patent 1 2,721,294 ELECTRON DISCHARGEDEVICES Earl l. Shelton, Natick, Mass., assignor to RaytheonManufacturing Company, Newton, Mass., at corporation of DelawareApplication March 9, 1951, Serial No. 214,796 Claims. (Cl. 31539.53)

This invention relates to electron discharge devices, and moreparticularly to devices of the magnetron type.

In copending application, Serial No. 66,249, filed December 20, 1948, byWilliam C. Brown, entitled Electron Discharge Device, there is discloseda cavity magnetron structure wherein alternating anode members areconnected by conductive strapping, and, in addition, groups of anodemembers have transmission lines connected in parallel with the strappingattached to said anode members, the transmission lines being connectedto the strapping at the end points of each group of anode members. Bythis type of group strapping, increased mode separation may be obtained,in particular, separation of the fundamental or 11' mode from theadjacent mode.

This invention discloses another type of group strapping wherein the endpoints of the groups of anode members are connected to a common junctionby means of transmission lines or conductors. Briefly, a structureembodying this type of group strapping may be made as follows. Amagnetron-anode structure has alternate anode members thereof connectedby a pair of conductive straps such that adjacent anode members areconnected to different of said straps. At a plurality of equally-spacedpoints along one of said straps, connections are made to a first commonjunction. Similarly, at a plurality of points along a second strap,connections are made to a second common junction, points of connectionon the first strap, and points of connection on the second strap being,respectively, adjacent, and the connectors connecting the points of saidstraps to the common junctions forming transmission lines. By thisstructure the overall phase shift, at a given percentage frequencydeviation from the 1r or fundamental mode, along the straps connectingthe anode members is substantially reduced.

In addition, this invention discloses that the output may be coupled tothe common junctions, for example, by means of a coaxial cable attachedthereto with the result that the anode structure will be substantiallysymmetrically loaded, thereby aiding in producing optimum operatingconditions for the discharge device.

Other and further objects and advantages of this invention will beapparent as the description thereof progresses, reference being had tothe accompanying drawings, wherein:

Fig. 1 illustrates a longitudinal, cross-sectional view of a magnetronembodying this invention;

Fig. 2 illustrates a transverse, cross-sectional view of the deviceshown in Fig. 1, taken along line 22 of Fig. 1; and

Figs. 3, 4 and 5 illustrate equivalent electrical circuits of portionsof the discharge device shown in Figs. 1 and 2;

Referring now to Figs. 1 and 2, there is shown an anode structurecomprising a metallic cylindrical member 11 which may be made, forexample, of copper. Extending radially inwardly from the inner surfaceof cylinder 11 is a plurality of anode vane members 12, said vanemembers 12 being substantially equally spaced circumferentially aroundsaid cylinder 11 and being made of metallic substantially rectangularplanar members whose planes are parallel to the axis of cylinder 11. Atpoints near the inner ends of vanes 12, on the top and bottom edgesthereof, conductive strapping 13 is connected between alternate anodemembers in a well-known manner such that adjacent anode members areconnected to diiferent straps.

2,721,294 Patented Oct. 18, 1955 "ice The pair of straps 13 at the upperedge of the anode members 12 is connected to additional conductive meansin the following manner. The innermost of the upper straps 13 isconnected at three equally-spaced points to the central conductor 14 ofa transmission line 15 by conductors 16. Similarly, at points adjacentthe connecting points on the innermost of the upper straps 13, theoutermost of the upper straps 13 is connected to the outer conductor 17of the coaxial transmission line 15 by means of conductors 18. As isshown here, by way of example, the innermost and outermost of the upperstraps 13 are each connected to the transmission line 15 at threeequally-spaced points. However, it is to be clearly understood that anynumber of connecting points can be used.

The upper end of cylinder 11 is covered by a pole piece 19 ofmagnetizable material such as an iron or steel alloy, said pole pieceextending inwardly and downwardly toward the inner edges of anodemembers 12, thereby forming a modified frustro conical shape. Holes 20are provided in pole piece 19 to allow the passage of the conductors 16and 18 therethrough without touching said pole piece 19. A metallicplate member 21 is sealed to the top of pole piece 19, the centralportion of member 21 being struck up to form a cylindrical member 22which surrounds the transmission line 15 but is spaced therefrom.Cylindrical portion 22 is sealed to the outer conductor 17 of thetransmission line 15 by means of a ceramic member 23, while the innerconductor 14 of the transmission line 15 is sealed to the outerconductor 17 thereof by a ceramic sealing member 24.

Inside the space defined by the inner edges of anode members 12 ispositioned a cathode structure 25 of any desired type, for example, asshown here, a cylindrical member whose outer surface is covered withelectronemissive material. End shields 26 are provided for said cathode,and are positioned slightly above and below the anode vane members 12 ina well-known manner. The lower end of the cylindrical cathode member 25is attached to alead-in cylinder 27 which extends through an opening ina lower magnetic pole piece 28. Magnetic pole piece 28 is substantiallysimilar to the upper magnetic pole piece 19 and is sealed to the lowerend of the anode cylinder 11. A metallic cylinder 29 is attached to thehole in the magnetic pole piece 28 through which the cathode support 27passes, said cylinder 29 surrounding support cylinder 27 but beingspaced therefrom. Cylinder 29 is sealed to cylinder 27 by means of aceramic sealing member 30. A conducting rod 31 extends up through thecenter of the support cylinder 27, and is connected to a heater coilpositioned in the cathode 25, the other end of the heater coil beingconnected to the cathode cylinder 25, and hence to support cylinder 27through cathode 25. Thus, by application of a potential between theconductor 31 and the support cylinder 27, current may be fed through thecoil to heat the cathode 25. Inner conductor 31 is sealed to the supportcylinder 27 by means of a ceramic seal 32.

An analysis of the group strapping action in this device will now bedescribed, reference being had to Figs. 3 through 5. Fig. 3 illustratesthe equivalent transmission line section of a group of anode members 12and the portions of the straps 13 associated therewith. Each group ofanode members and associated strap portions 13 between points ofconnection of the straps 16 and 18 to the strapping 13 will be termed ananode section. As shown here, this anode section may be represented by atransmission line having a series impedance W and two equal shuntimpedances X and X connecting each side of the impedance W to theopposite of the transmission line. If one end of the transmission linelabeled E and F is at one point of connection on a pair of conductors 16and 18 to adjacent points on the strapping 13, and the other end 3 ofthe transmission line indicated. by points C and D indicates points ofconnection of another pair of conductors 16 and 18 to points on thestrapping 13 separated by an anode section, then the series impedance Wis equal to:

W=jZm sin (N/3 13m) and X=-]'Zm cot (N/3 [rm/2) (2) where Zm is thecharacteristic impedance of the group anode section, [3m is the phasefunction or phase shift across one anode cavity defined by one pair ofadjacent anode members 12, and N is the number of anode members.

In Fig. 4, there is shown an equivalent transmission line for each ofthe pairs of straps 16 and 18 connecting adjacent points of thestrapping 13 to transmission line 15, each pair of straps 16 and 18forming a susbtantially parallel wire transmission line. If one end ofthe transmission line, as indicated'by points E and F in Fig. 4,represents the points of connection of the conductors 16 and 18 to thestraps 13, and the points A and B at the other end of the line in Fig. 4indicate the points of connection of. the conductors 16 and 18 to innerand outer conductors 14 and 17, respectively, of the transmission line15, then the transmission line comprising conductors 16 and 18, asindicated in Fig. 4, may be represented by an equivalent 1r sectionnetwork having a series impedance Y and two shunt impedances Zconnecting either end of series impedance Y to the other side of thetransmission line. The values of Y and Z may be ascertained as follows:Y=jZz sin [32, Z: jZz cot ,82, where Z1 is the characteristic impedanceof the transmission line comprising conductors 16 and 18, and [31 is thephase shift per unit length along said transmission line.

In Fig. 5, there is shown the equivalent overall circuit of the groupanode sections of the type illustrated in Fig. 3 and the connectingtransmission line sections of the type illustrated in Fig. 4. At threepoints there are junctions between two adjacent anode sections and atransmission line section and consequently there are three impedanceslabeled a which represent the parallel combination of two Xs and Z. Theupper line has three impedances d which arethe impedances W of Fig. 3.The common junction of all the points A and B of Fig. 3 has connectedthereacross an impedance C which is the parallel combination of threeZs. The impedance of the transmission line 15 of Fig. 1 which isconnected to this structure is omitted for the purposes of this analysisin the interest of simplification. However, it could be included, ifdesired, in a more rigorous analysis. The impedances b represent theseries impedances of the transmission lines of Fig. 4, and are equal tothe impedance Y therein. If six currents are assumed to flow in variousmeshes of the 'network illustrated in Fig. 5, said currents beingnumbered I1 through I6, inclusive, network equations may be written andsolved in accordance with Kirchhoffs laws. These equations are writtenfor convenience in matrix form as follows:

E a a 2a+d --a a 14 E5 0 a -a a 2a+d a 1.;

E a 0 a a -a 2a+d is The solution of this-matrixby means of determinantsand the equating of the solution to Zero yield the natural resonantfrequencies of the system. The solution of the determinate is:

Substitution of the impedance Formulas l and 2 in 4 and factoring yieldthe following significant formulae:

where A is a constant for a particular number of anode sections and isdetermined from the matrix. For three sections, A+l equals zero, forfour sections, A (A+2) equals zero, and for five sections, A |A+1 equalszero. in these formulae, N equals the total number of anode vanemembers, and S equals the number of anode sections. Incorporation ofthis type of strapping into a twelve-anode member magnetron yielded thefollowing results: a-lculationof the mode separation of the adjacentmode from the 7r mode produced an increase of mode separation fromfifteen point five per cent to twentytwo point five per cent. Testing ofthis device indicated that the mode separation was actually increased totwentyfour point three per cent by this structure.

Thus,v it may be seen that, by the addition of group strapping by meansof parallel wire transmission lines connected to a common junction, adistinct improvement in power-producing capabilities and hence theoperating efficiency of the device may be achieved.

This completes the description of the embodiment of the inventiondescribed herein. However, many modifications thereof will be apparentto persons skilled in the art without departing from the spirit andscope of this invention. For example, any desired number of anode vanemembers andanode groups may be used. Any desired output may be attachedto the common junctions as, for example, probes or loops for excitingwaveguides, and, indeed, the output need not necessarily be taken fromthe common junctions but may be taken out of the anode members by a loopor probe coupling in a conventional manner. Accordingly, it is desiredthat this invention be not limited by the particular embodimentdescribed-herein,-except as defined by the appended claims.

What iselaimed is:

1. An electron discharge device comprising a cathode and an anodestructure radially spaced from said cathode, a pair ofconductive straps,each of said straps connecting, respectively, diiferent alternate anodemembers together, a coaxial energy outputcoupling structure, andseparate conductors connecting a plurality of circumferentiallyspacedpoints on each of said straps to said output structure.

2. An electron discharge device comprising a cathode and an anodestructure radially spaced from said cathode, a pair of conductivestraps, each of said straps connecting, respectively, dififerentalternate anode members together, a coaxial energy output couplingstructure, and separate conductors connecting a plurality ofcircumferentiall-y spaced points-on each of said straps to said outputstructure, each adjacent pair of said separate conductors formingtransmission lines.

3. An electron discharge device comprising a cathode and an anodestructure radially spaced from said cathode, a pair of conductivestraps, each of said straps connecting, respectively, diiierentalternate anode members together, a coaxial energy output couplingstructure, and separate conductors connecting aplurality ofcircumferent-ially spaced points on each of said straps to said outputstructure, the points of connection of said con-ductors to said strapsbeing arranged in pairs of adjacent points, one of each of said pairs ofpoints being on one of said straps and the other of each of said pairsof points beingon-an adjacent'strap.

4. An electron discharge device comprising a cathode and an anodestructure radially spaced from said cathode, a pair of conductivestraps, each of said straps connecting, respectively, differentalternate anode members together, a coaxial energy output couplingstructure, separate conductors connecting a plurality ofcircumferentially spaced points on each of said straps to said outputstructure, and means for producing a magnetic field substantiallytransverse to the direction of motion of electrons moving from saidcathode to said anode structure.

5. An electron discharge device comprising a cathode and an anodestructure radially spaced from said cathode, a pair of conductivestraps, each of said straps connecting, respectively, difierentalternate anode members together, a coaxial energy output couplingstructure, and separate conductors connecting a plurality ofcircumferentially spaced points on each of said straps to said outputstructure, the points of connection of said conductors to saidReferences Cited in the file of this patent UNITED STATES PATENTS1,558,120 Simpson Oct. 20, 1925 2,103,638 Posthumus Dec. 28, 19372,111,263 Fritz Mar. 15, 1938 2,169,725 Fritz Aug. 15, 1939 2,428,612Blewett Oct. 7, 1947 2,478,534 Kather Aug. 9, 1949

